src: add process.versions.icu

If i18n support is present, add the icu version
to process.versions

Fixes: https://github.com/nodejs/node/issues/3089
PR-URL: https://github.com/nodejs/node/pull/3102


Reviewed-By: Steven R Loomis <srloomis@us.ibm.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Rod Vagg <rod@vagg.org>